This proposed research is intended to characterize the catecholamine-synthesizing enzyme, dopamine-beta-hydroxylase, (DBH), as it pertains to humans. This goal will be accomplished by 1. isolating the enzyme from human plasma, as well as other human tissues such as adrenal gland and pheochromocytoma, 2. conducting physicochemical comparisons of the molecular properties of these enzymes, and 3. developing a radio-immunoassay specific for human plasma DBH in order to help define the relationship of plasma DBH to sympathetic nervous system activity. Furthermore, direct comparison of the biochemical and immunological characteristics of the various forms of human DBH as well as the enzyme isolated from other sources, such as the bovine adrenal gland, will be performed. Both the enzymatic assay of DBH and the immunochemicla titer of this enzyme in human plasma will be directly assessed in clinical studies on essential hypertension in man.